New, brighter types of supernovas challenge widely accepted theories

In recent years, two new supernovas have been observed which don't act like supernovas usually do. New, more effective scanning telescopes are catching new behaviours. The observations challenge current theories about how massive stars die. Two new studies, published in the journals Nature and Nature Astronomy, presenting the findings have Stockholm University researchers among the co-authors.

Nordic Optical Telescope.

Supernovas are exploding stars. The most common is "Type II," which consist mostly of the universe's most common element, hydrogen. For the past 10 years most research has focused on less common types of supernovas. Scientists thought that they already understood Type II supernovas that come from red giant stars, which are common.

When more and more supernovas were uncovered by new, effective scanning telescopes, however, researchers started to notice explosions that didn't fit with existing theories. The Palomar Observatory in California discovered Supernova iPTF14hls about three years ago, in September 2014. Among the hundreds of Type II supernovas found with their telescopes, this one didn't seem so remarkable. However, instead of dimming like normal Type IIs, this one suddenly got brighter. It's also undergone a number of eruptions in the past few years - something that was unprecedented.

In the same year, another telescope found Supernova OGLE-2014-SN-073, which was also thought to be a normal supernova. This one, however, not only grew brighter but also exhibited faster speed. Taken together, this requires much more energy than calculated by current theories of supernovas.

"Both of these explosions challenge our current theories on how massive stars die. Because they don't fit, the theorists have to go back to the drawing board and evaluate their models," says Jesper Sollerman, Professor of Astronomy at Stockholm University. "OGLE-73 will likely expand the model, while iPTF14hls certainly will require totally new thinking."

"Supernova iPTF14hls is still burning so brightly that we can actually follow it with the Nordic Optical Telescope at La Palma," adds Francesco Taddia, Postdoctoral Researcher in Astronomy, Stockholm University. "Now we will use the Hubble Telescope to look at it in time for Christmas."

The results of the research are presented in two articles, one in Nature and one in Nature Astronomy.